The present invention is an improvement on the invention disclosed and claimed in U.S. Pat. No. 4,046,106, which was issued to Bowman, Sept. 6, 1977, before the filing of the application on the present invention. The improvement greatly extends the capabilities of the machine disclosed in the aforementioned patent, although the improvement involves only a relatively minor change to one part of the machine. Because the changed part would have no forseeable utility apart from the machine, the description of the machine given in U.S. Pat. No. 4,046,106 will be repeated herein with only such minor alterations as are required to make the description consistent with the improvement. Readers already familiar with the machine will find it expeditious to proceed directly to the portions of the description bearing the headings "Summary of the Invention" and "The Improvement of the Present Invention."
Patch type self-locking fasteners in which a plastic patch is adherently bonded to the threads of the fastener are now being used in a wide variety of applications. For example, patch type fasteners are widely used in the aircraft industry and also the ophthalmic industry.
Patch type fasteners are particularly useful in applications where, through vibration or the application of recurrent forces, there is a tendency for the fastener elements to become unthreaded. Where this occurs, the structural members which are held together by the fastener elements may then become separated. In use applications, such as in an aircraft structure, the separation of structural members could be very harmful.
In a patch type self-locking fastener, one of the fastener elements, such as an externally threaded bolt, has a plastic patch which is adherently bonded to a portion of the screw threads of the bolt. When the bolt is then inserted into a complementary female element, the engagement of the plastic patch with the internal threads of the female element produces an increase in the frictional force between the male and the female elements. When the elements are in threaded engagement, the elements may, then, be subjected to vibrational or otherwise recurring forces without loosening of the threaded engagement between the fastener members. If it is desired to disengage the fastener element, this can be accomplished by applying a torque to the male or female fastener elements with a suitable hand tool. Since the plastic patch is adherently bonded to the threads of the self-locking fastener, the fastener member may be reused a number of times without adversely affecting the bond of the patch to the fastener threads and the performance of the fastener element in providing a firm locking connection with a complementary threaded member.